hameg-hmo: Fix two compiler warnings (-Wstringop-truncation).

hameg-hmo: Fix two compiler warnings (-Wstringop-truncation).

  src/hardware/hameg-hmo/protocol.c: In function ‘hmo_scope_state_get’:
  src/hardware/hameg-hmo/protocol.c:1130:2: warning: ‘strncpy’ specified bound 20 equals destination size [-Wstringop-truncation]
    strncpy(state->trigger_pattern,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     sr_scpi_unquote_string(tmp_str),
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     MAX_ANALOG_CHANNEL_COUNT + MAX_DIGITAL_CHANNEL_COUNT);
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    CC       src/hardware/hp-3478a/api.lo
    CC       src/hardware/hung-chang-dso-2100/protocol.lo
  src/hardware/hameg-hmo/api.c: In function ‘config_set’:
  src/hardware/hameg-hmo/api.c:388:3: warning: ‘strncpy’ specified bound 20 equals destination size [-Wstringop-truncation]
     strncpy(state->trigger_pattern,
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      tmp_str,
      ~~~~~~~~
      MAX_ANALOG_CHANNEL_COUNT + MAX_DIGITAL_CHANNEL_COUNT);
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~